1. Field of the Invention
This invention relates to digital maps of the type for displaying road or pathway information, and more specifically toward a method for updating information contained in a digital map using reliable probe data.
2. Related Art
In nearly all developed and developing countries, roadways are becoming more congested and as a result travel times are increasing. The need for accurate and timely traffic information continues to grow. Such need has encouraged the rise of personal navigation devices which utilize digital maps combined with accurate positioning data. Commuters seeking navigation assistance have embraced this emerging technology, trying to avoid traffic jams and for businesses trying to minimize transportation costs. The effectiveness of such navigation systems is inherently dependent upon the accuracy and completeness of its digital map data and other provided information.
In the current field of personal navigation systems these Personal Navigation Systems (PNAV), like dedicated handheld navigation systems, Personal Digital Assistance (PDAs), mobile telephones provided with a navigation module, as well as the in-car navigation market, end-user needs are already commonly addressed by many applications. Vendors differentiate by adding additional functions and features to their PNAV. Examples include speed camera information, traffic information, junction views, and the like. Such additional features of PNAV assist the user in taking the correct decisions when traveling from a starting location to a destination. One approach is illustrated by way of example in FIG. 1 which presents one possible display screen of a PNAV device. A bird's eye map may be shown on one portion of the screen together with a junction view, i.e., a depiction of all lanes and side posts as are present in reality superimposed with additional information such as arrows, route indications and the like.
Sometimes, a driver or navigator will make decisions as to which particular route to follow based on a comparison of the estimated travel time and/or ease between two or more alternative routes. For example, FIG. 2 illustrates an exemplary digital map having a starting point 12 and a destination point 14. Two alternative routes are depicted, one representing a slightly shorter travel distance but longer travel time which is not preferred. Rather, the preferred route occupies a shorter projected travel time even though its total travel distance is slightly longer.
Navigation decisions of this nature are highly dependent upon the allowable speed limits for the various road segments connecting the starting and destination points. For example, referring again to FIG. 1, the bird's eye digital map view shown on the left hand side of the display screen includes speed limit indications 16 along several of the depicted road segments. Thus, a navigator's decision which course to follow may be decided as a function of the indicated speed limits 16. Furthermore, a driver's ability to comply with posted speed limits is sometimes dependent upon knowing what the speed limits are on the particular road segment being traveled. Sometimes, a roadside sign indicating the local speed limit may not be visible. If the particular road segment is unfamiliar to the driver, the speed limit may not be readily apparent. By reference to the information provided on a PNAV, like that illustrated in FIG. 1, the user's current position is matched to a particular road segment contained in the digital map, and the speed limit indication for that road as stored in the memory device of the PNAV may be displayed for the safe driving benefit of the driver.
Road speeds for passenger vehicles are only one attribute which is useful to know and have provided in a PNAV device. For another example, one may consider heavy truck/lorry maximum speeds which could be different than passenger vehicle limits. Another example of useful attribute could be the location of service vehicle stops such as taxis, buses, and the like. Of course, many other road attributes could also be identified in these contexts, and are not limited to vehicle speeds and stops for service vehicles.
It will be appreciated, therefore, that digital map data is more valuable when its information content is accurate and complete. Certain attribute specifications for road segments, such as posted speed limits, taxi stops, road geometries, point of interest (POI) information and the like may be included in association with particular road segments, junctions or other features of a digit map for all of these reasons.
Road positions and attributes are constantly changing. New roads are created, old roads are discontinued, construction activities create temporary blockages and unusual detours, speed limits change, bus and tax stop positions are moved, and the like. Accordingly, there is a continuing need to update digital maps with the latest and most current information available, including information about attributes such as speed limits, taxi and bus stops, road geometries and POI information. There is therefore a need for improved methods for updating digital maps so that the information contained in them will be current and of the maximum possible value to users of PNAV systems.